The monitoring of blood glucose concentration is an essential part of the daily routine of diabetics. The blood glucose concentration has to be determined quickly and reliably several times a day in order, if appropriate, to be able to take suitable medical measures. So as not to restrict the diabetic's daily routine any more than is necessary, suitable portable devices are often employed which are intended to be easy to carry around and to operate, such that the blood glucose concentration can be measured, for example at the workplace or even during leisure time.
Various portable devices are presently available on the market, some of them functioning according to different measurement methods, for example optical or even electrochemical measurement methods. An example of a frequently employed measurement method utilizes a special kind of electrochemical test strips. These test strips are, for example, configured such that a predetermined quantity of blood is conveyed to an electrode system via a capillary system on the test strip. For modern test strips, a quantity of blood of ca. 1.5 μl is sufficient, sometimes even quantities of blood of less than 1 μl. The electrode system may, for example, comprise metal electrodes that are provided with a reagent coating. The reagent coating in most cases contains different enzymes and so-called mediators and has the effect that charge carriers (for example in the form of redox molecules) form within the sample. The number of these charge carriers depends on the blood glucose concentration, and can be determined by means of the electrodes and a suitable measurement system, for example by means of a current-voltage measurement. From the amount of charge carriers, it is possible, finally, to calculate the blood glucose concentration. An example of electrochemical test strips of this kind is set out in U.S. Pat. No. 5,286,362, which is hereby incorporated by reference herein in its entirety.
As an alternative to the described electrochemical measurement method, other measurement principles can also be used. Thus, for example, WO 01/48461 describes a test strip with light guides for examining a sample, in particular of a body fluid, in which a reagent system, upon reaction with the sample, leads to a characteristic and optically measurable change in a detection zone. Light guides provided on the test strip allow the optical change to be remotely evaluated by an evaluation device.
The test strips thus form an important element of portable diagnostic systems. Typically, about 5 to 7 such test strips are needed each day by a diabetic. It is essential that the test strips are stored in a clean and dry condition, to ensure that the measurement of the blood glucose concentration is not rendered inaccurate by contamination or by the effect of moisture on the reagent coating or reagent system.
For this purpose, the test strips are usually stored in suitable containers in order then to be removed by the user from the test strip container for a measurement and fitted into a corresponding measuring device. Such measuring devices, for example measuring devices for electrochemical determination of the blood glucose concentration, are known to persons skilled in the art and are described, for example, in US 2002/0170823 A1 or in WO 96/30752, each of which is hereby incorporated by reference herein in their entireties.
However, the measuring systems known from the prior art, in which a blood glucose concentration is determined by means of a single test strip (single strip systems) and in which an individual test strip for a measurement has to be inserted into the device, have numerous disadvantages in practice. Such systems require numerous steps to be performed by the user or patient. A test strip has to be removed from a suitable storage device (e.g. a box of test strips) and then manually inserted into a measuring device. Thus, in order to permit secure handling by a patient, in particular by elderly patients or children, a corresponding test strip for single-strip systems of this kind can be made relatively large, in order to avoid the test strip slipping from the user's fingers and not being able to be used for a measurement. An increased size of the test strips, however, has the effect that the space taken up by the measuring systems increases and fewer test strips can be accommodated in a corresponding container. This increased space requirement also increases the material costs of the measuring systems.
The manual handling of the test strips is also associated with the disadvantage of increased risk of contamination of the test strips. Thus, manual removal of the test strips from a test strip container can expose the test strips to sweat on the fingers or to other forms of contamination that could impair a corresponding measurement. A further considerable disadvantage is that, each time the test strip container is opened, the test strips remaining in the test strip container are exposed to air moisture, with the result that test strips later removed from a test strip container will possibly have different properties than the test strips that were removed first.
In order to avoid the disadvantages of single-strip systems of this type, integrated systems have bean developed, in particular systems in which, in addition to a measuring device, a magazine for test strips is also incorporated. The systems can be designed in such a way that a test strip required for a measurement is in each case dispensed from the magazine to a measurement position. After application of the suitable sample thereto, for example a drop of blood, the measurement is then carried out directly.
Examples of integrated systems of this kind are described in WO 02/18940 A2, EP 1 488 736 A1, and EP 1 507 143 A1.
Compared to conventional single-strip systems, integrated systems have considerable advantages. For example, the number of steps needed to carry out a measurement is reduced, and it is also possible to use small, inexpensive test elements. The exposure of the test elements, in particular the test strips, to moisture and contaminants is also considerably reduced.
However, the integrated systems known from the prior art also have disadvantages, particularly disadvantages that detract from their use as portable devices and that reduce the level of acceptance by the patient. An important disadvantage is that the integration of the systems leads to comparatively large sizes of the devices. For example, for many integrated systems, bulky spring systems are needed to permit corresponding transport of test strips from a storage position to a measurement position. Other integrated systems may be driven by an electric motor, which requires even more space. By contrast, integrated systems not driven by electric motor require additional manual tensioning devices, which in many cases makes handling difficult, particularly for elderly patients or children. Moreover, the production costs of the systems are greatly increased when using electric motor drives or complex manual drives. Electrically driven systems additionally have the disadvantage that powerful batteries are needed for the electric motors, and these powerful batteries are expensive and have to be changed frequently. These batteries additionally lead to a further increase in the volume of the structure. A further disadvantage of the complex integrated systems known from the prior art is that these systems often have sensitive components on their surfaces, which components may easily be mechanically damaged, for example when the device is carried in a pocket, allow moisture to penetrate into the devices, and/or may be functionally impaired by contaminants.
While the foregoing describes systems designed for measuring blood glucose concentration, similar circumstances exist for other diagnostic and other analyte measuring devices and systems. It will be recognized that the shortcomings of the prior art and the objects of the present invention apply not just to blood glucose monitoring systems.
In view of the foregoing, it is an object of the present invention to provide a test device for determining at least one analyte concentration in a sample, in particular a liquid sample, by means of at least one test element, which test device avoids the disadvantages of the test devices known from the prior art. Moreover, another object is to provide corresponding test elements that can be used with the test device according to the invention.